CNC machine tools

ABSTRACT

This device is a computer numerically controlled (CNC) machine tool such as an edge grinding apparatus. More specifically, the device is a CNC apparatus for processing blanks such as a glass sheet. The device uses a sensor to program the path of the grinding wheel. The system requires a CNC machine, a sensor such as a laser and software to calculate the offset parameters.

TECHNICAL FIELD

[0001] This apparatus relates to computer numerically controlled (CNC)machine tools such as an edge grinding apparatus. More specifically, theinvention relates to a CNC apparatus which uses a sensor such as a laserfor processing blanks such as a glass sheet.

BACKGROUND ART

[0002] Machine tools such as an edge grinding apparatus include at leastone grinding wheel, at least one rotatable holder for a blank, and atleast one CNC device for controlling the grinding of the blank accordingto selected specification. The CNC machine tool may include amulti-axis, linear (X, Y axis) holder instead of a rotatable holder. Ineither case, a cutting tool moves relative to the blank or workpieceunder the control of a programmable controller, including a computerprogram.

[0003] In a standard CNC glass grinding machine, an operator must adjustthe CNC parameters to allow the CNC machine to grind the part where itis located on the machine. This can be a slow process and is difficultfor many operators to master. The prior art process requires theoperator to grind a part, check the part for even grind then adjust theX, Y and rotation offset parameters on the CNC control to move the CNCprogram to match the part location.

[0004] U.S. Pat. No. 5,588,899 discloses one solution to this problem.

[0005] The apparatus of this patent is an opto-electronic device forpositioning eye glass or spectacle lenses in a CNC grinding device. Theopto-electronic detecting device includes a CCD (charge coupled device)camera, a first control unit that includes an electronic pictureprocessing and evaluating system cooperating with a second control unit.The system requires the manufacturer of the lens blank to mark eachblank. If the blanks are not pre-marked, a separate marking isnecessary.

[0006] U.S. Pat. No. 5,956,253 discloses a more recent development whichuses a video controlled CNC apparatus for processing blanks such as aglass sheet. The device uses a video camera and monitor to program thepath of the grinding wheel. The system requires a CNC machine, videocamera, a video monitor, a vision board and software to calculate theoffset parameters.

DISCLOSURE OF INVENTION

[0007] The device of this invention uses a high accuracy sensor tolocate and program the path of the grinding wheel rather than positionthe blank in the CNC grinding device. No pre-marking or separateprocessing steps are needed. The system requires a CNC machine, a highaccuracy reflective sensor and software to calculate the offsetparameters. An operator must initiate a load cycle. Once the part isloaded on the CNC machine, the operator must start the measurementcycle. The measurement cycle will move a sensor such as a laser alongthe program path, stop at each of the checkpoints, and find the edge ofthe glass. The system software will store the edge of the glass andreport the position to the CNC control. The control will continue thiscycle through all the checkpoints. When the part path is complete thecontrol will calculate the required offsets. Thereafter, the system willprocess additional blanks automatically without repeated adjustments foreach blank.

[0008] The sensor may be a through beam or reflective type beam. It alsocould be inferred, ultrasonic or laser beam. Reflective lasers may bethe best choice because they have a very small beam diameter, not easilyaffected by water or dirt, reasonable cost, and can see most materialswell. The laser does not require the software power of the camerasystem. Also, the laser operates with or without hard stops. The laseris especially useful with many different sized parts, irregular edges orspacially curved edges (rear view mirror). The glass or blank acts as areflective surface for the laser.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a side elevational view of an edge grinding apparatusaccording to the present invention having a rotatable holder.

[0010]FIG. 2 is a side elevational view of an edge grinding apparatusaccording to the present invention having a multi axis, linear holder

[0011]FIG. 3 is a top elevational view of the apparatus of FIG. 2.

[0012]FIG. 4 is a fragmentary side view of FIG. 1 showing the videocamera and fastener in greater detail.

[0013]FIG. 5 is a logical flow chart illustrating the operation of theinvention.

[0014]FIG. 6 is a logical flow chart illustrating the operation of theinvention.

BEST MODE OF CARRYING OUT INVENTION

[0015] The CNC machine tool and high accuracy sensor are standard items,but the use of the sensor to control the path of the cutting tool in CNCmachine tools is new. Software calculates the CNC offsets for themachine control. The sensor system finds the intersection of a minimumof two X plane and two Y plane programmed gridlines with the partperimeter. The CNC software must then calculate the real position of theintersections as compared to the positions in the sensor.

[0016] The software operation is as follows.

[0017] 1. User initiates measurement of the part.

[0018] 2. The control positions the sensor over the part.

[0019] 3. The control searches for the edge of the part.

[0020] 4. The control stores the position data.

[0021] 5. The control calculates a new position to place the sensor.

[0022] 6. The control positions the machine over the next point.

[0023] 7. The control repeats steps 3 and 6 until the start point isreached.

[0024] 8. The control initiates on optimize sequence to reduce themeasured points to arcs and lines that can be used to control themachine in production.

[0025]FIG. 1 is a side elevational view of CNC edge grinding apparatus10. Apparatus 10 subjects a generally planar article or blank S such asa sheet of glass to an edge grinding operation in an endless patternaround the periphery of the article. Blank S may have an irregularshape. Rotatable table 12 includes clamp 14. Frame 16 supports table 12,as well as the other components of CNC apparatus 10. Servo motor 18drives or rotates table 12 through drive shaft 20 which connects motor18 to table 12. Motor 18 rotates table 12 and blank S 360° about theI-I′ axis. Lift cylinder 22 houses lift ram 24 which connects to clamp26. Cylinder 28 raises and lowers ram 24 and clamp 26 in a verticaldirection to predetermined set points along I-I′ axis. Clamp 14 andclamp 26 sandwich blank S therebetween when cylinder 28 lowers clamp 26to hold blank S in position against clamp 14.

[0026] Frame 16 also supports frame 30 and frame 30 in turn supportslift cylinder 22, servo motor 32 and edge grinder assembly 34. Servomotor 32 is connected to assembly 34 by drive shaft 36. Motor 32 movesassembly 34 horizontally on a straight line towards and away from blankS along the II-II ′ axis.

[0027] Edge grinder assembly 34 includes grinding wheel 36 and grindingmotor 38. Motor 38 is rotatably connected to wheel 36 through driveshaft 40. Motor 38 rotates wheel 36 in a complete circle 3600 about theIII-III′ axis.

[0028] Housing 42 surrounds motor 38. Housing 42 has an outside surfaceand laser 44 is attached to the outside surface of housing 42 withappropriate fasteners.

[0029]FIGS. 2 and 3 shows CNC edge grinding apparatus 10 adapted forlateral, linear movement of a blank towards grinder assembly 34.Rotatable table 12 and its components are replaced with load table 50.Positive stops 52 and 52′ are located on frame 54 which carries table50. Motor 56 connects to table 50 through drive 58. Motor 56 moves table50 back and forth horizontally in a straight line along IV-IV′ axisbetween stops 52 and 52′.

[0030]FIG. 4 shows sensor 44 mounted on quick disconnect fastener 60.This keeps sensor 44 clean during production. Quick connect 60 uses twoplates 62 and 64. One is mounted to sensor 44 and one to housing 42.Precision alignment pins 66 mounted to camera plate 62 and precisionholes 68 in machine plate 64 make camera placement repeatable within+/−0.001″ (0.025 mm). Machine plate 64 is slotted so the camera positioncan be adjusted during calibration. The center of sensor 44 may bealigned with +/−0.002″ (0.05)mm of the center line of the spindle. Thedistance from the center of wheel 34 is measured within 0.001″.

[0031] Sensor 44 is electrically disconnected with a connector 70 oncable 72 for the signal and power.

[0032] While the power of sensor (laser) 44 may vary widely, I prefer alower power laser in the milliwatt range with a class 2 laser productsafety rating. Generally, the laser has a power of less than 25milliwatts and preferably less than 10 milliwatts. The laser I used wasless than 1 milliwatt.

[0033]FIGS. 5 and 6 are logical flow charts illustrating the operationof the CNC machine and sensor. FIG. 5 is the part location process toestablish edge points of blank S. FIG. 6 is the digiting system tocreate a production program for moving grinding wheel 34 around theperimeter of blank S. FIGS. 5 and 6 show the step of removing the sensorbefore starting production. In an alternative embodiment, the operatorcould enclose the sensor rather than remove it. These steps are neededmerely to keep the sensor clean and to prevent damage. Particles from atooling operation such as edge grinding could interfere with thesensor's operation.

[0034] While grinding illustrates the machining operation, the sensorcontrolled CNC machine can perform other operations such as cutting anddeleting (removing paint or printing from a part).

[0035] CNC apparatus 10 also may include a shuttle with a vacuum pick upunit mounted on linear motion ways. The pick is air cylinder actuatedfor raising and lowering. The function of the shuttle is to pick upparts from the cutting conveyor, break-out the excess trim of the part,and shuttle the parts to the grinding station. Break-out fingers areused to remove the excess glass around the part; once this operation hasbeen completed the fingers retract to facilitate picking up the part.The lateral movement of the shuttle between the pick up station and thegrinder load table is a fixed distance for all parts. Positive stops areprovided to slow the cylinder at the end of each stroke and stop thepick up device in an exact location at either end of its travel. Thisassures positive location of the part in the system.

[0036] Edger 36 is a three axis, continuous path CNC edge grinderdesigned specifically to run auto glass or similar parts. The diamondwheel grinds 360° degrees; after the part is ground, the diamond wheelretracts and the belts raise up to shuttle the part out. Linear motionof the slides is controlled by an A.C. servo motor and a directlycoupled, bail type lead screw. Lead screws on both the “X” and “Y” axesare mounted in pre-loaded, angular contact, high thrust type bearings toeliminate all end play. Mounted on the spindle carriage assembly (“X”axis) is a precision grinding spindle directly coupled to a 5 H.P., A.C.drive motor. Also attached to the housing that holds the spindle is avacuum type coolant guard assembly and rotating mechanism. This assemblyconsists of the necessary components, bearings, seals, gears and an A.C.servo motor to rotate the guard to keep its slotted opening tangent tothe point of grind. The vacuum coolant guard also contains a coolantspray ring which directs coolant to the diamond wheel. When grinding,coolant is piped to this ring from an external supply. The rotatingfeature of this assembly comprises the third axis of the machine. Thediamond wheel is mounted on a motorized, balanced, variable speedspindle.

[0037] As table 50 and blank S move towards stop 52′, the endless motionof grinding wheel 36 circumscribes a portion of the periphery of theblank. As table 50 and the blank reverse direction, grinding wheel 36continues on its path about the periphery of blank S. When table 50stops a stop 52, the grinding path is complete

[0038] The CNC electrical cabinet consists of all components necessaryto control the compact system. In the main enclosure is housed the CNCcontroller, servo amplifiers, the program logic controller and theadjustable frequency A.C. motor drives and other components necessaryfor the manual and automatic operation of the compact system. The CNCcontroller used is a dual CNC continuous path control that controls theX, Y and Z (coolant guard rotation) axes.

[0039] The machine is equipped with a vacuum coolant guard and a mistcollection system designed to keep coolant off the glass and the machineguards. The vacuum guard itself has a fixed rear section and an easilyremovable front half; coolant and air are pulled up through the top ofthe guard and up to the mist collector via flexible hose. Once thegrinding cycle is completed, a belt section will raise to convey toglass to the next process. The PLC will control the non-motion functionsof the CNC and the table. It will also interface with the line controlpanel to insure automatic sequencing of the line. In the doors of thepanel will be push buttons and selector switches that allow manual andautomatic control of the CNC grinder.

[0040] In a standard CNC glass grinding machine, an operator must adjustthe CNC parameters to allow the CNC machine to grind the part where itis located on the machine. This can be a slow process and is difficultfor many operators to master. The prior art process requires theoperator to grind a part, check the part for even grind then adjust theX, Y and rotation offset parameters on the CNC control to move the CNCprogram to match the part location. This normally require manyiterations at about 30 to 60 seconds per pass. Operators can easily makeerrors that may damage the machine or grinding tool and make the processtake much longer. Also, operators may make imperfect adjustments duringset up causing excess tool wear, lower throughput and lower yields.

[0041] By using a sensor such as a laser and programming check points inthe CNC program, the operation can be automated. The CNC machine canthen automatically go to the check points and measure the part location.Once the locations are measured, the CNC control can calculate thenecessary X, Y and rotation offset parameters. This removes the chancefor operator error, increases the accuracy of part positioncompensation, finds the parameters in one pass and does not waste glassfor set up.

I claim:
 1. An apparatus for tooling a blank, the apparatus comprising acomputer numerically controlled machine having: a holder having a blankmounted thereon, the blank having edges; a tool assembly including atool for tooling the blank; a plurality of machine members and aplurality of programmable controllers movable under the control of aprogram to cause relative movement of the tool so as to cause the toolto move along a programmed path relative to the blank, the plurality ofmembers and controllers including; a sensor attached to the toolassembly and positioned over the blank; a controller that initiatesmeasuring the blank; a controller that positions the sensor over theblank; a controller that finds the edges of the blank with the sensor; acontroller that calculates a plurality of points on the blank; a controlthat calculates a new position for the sensor; a control that positionsthe sensor over the next point; a control that repeats the steps until aplurality of points on the blank is reached; and a control thatinitiates tooling of the blank using the calculated points from thefinding of the edges of the blank.
 2. An apparatus according to claim 1wherein the sensor is a high accuracy sensor.
 3. An apparatus accordingto claim 2 wherein the sensor is a reflective sensor.
 4. An apparatusaccording to claim 3 wherein the sensor is a laser.
 5. An apparatusaccording to claim 1 wherein the tool assembly includes a housing andthe sensor is attached to the housing.
 6. An apparatus according toclaim 5 wherein a quick disconnect fastener attaches the sensor to thehousing.
 7. An apparatus according to claim 6 wherein the quickdisconnect fastener is a pair of co-operating mounting plates, one platebeing attached to the housing and one plate being attached to thesensor.
 8. An apparatus according to claim 7 wherein one plate includesprecision alignment pins and one plate includes precision alignmentholes.
 9. An apparatus according to claim 8 wherein the pins of oneplate engage a portion of the holes of one plate when the sensor isattached to the housing.
 10. An apparatus according to claim 9 whereinone plate includes slots to facilitate the attachment.
 11. An apparatusaccording to claim 1 wherein the holder is a rotatable holder or amulti-axis, linear holder.
 12. An apparatus according to claim 1 whereinthe tool is an edge grinder.
 13. An apparatus according to claim 1wherein the blank is a sheet of glass.
 14. An apparatus according toclaim 1 wherein the blank has an irregular edge.
 15. A process forestablishing data for a programmed path for tooling a blank comprisingthe steps of providing a computer numerically controlled machine, a toolassembly including a tool for tooling the blank, and a plurality ofmachine members and a plurality of programmable controllers moveableunder the control of a program to cause relative movement of the tool soas to cause the tool to move along a programmed path relative to theblank; placing a blank having edges on the machine; attaching a sensorto the tool assembly and positioning it over the blank; initiating ameasuring cycle of the blank; positioning the sensor over a point on theblank; finding the edges of the blank with the sensor; calculating aplurality of points on the blank; storing the calculated points;calculating a new position for the sensor; positioning the sensor overthe next point; repeating the steps until a plurality of points on theblank are reached; and initiating the tooling of the blank using thecalculated points from the finding of the edges of the blank.
 16. Aprocess according to claim 15 wherein the step of tooling the blank isthe step of edge grinding a glass blank with an edge grinder.
 17. Aprocess according to claim 15 wherein the step of finding the edges withthe sensor is moving the sensor over the edges of the blank andrecording the position of the sensor transition.
 18. A process accordingto claim 15 wherein a laser finds the edges of the blank.
 19. A processfor tooling glass comprising the steps of providing a computernumerically controlled machine, a tool assembly including a tool fortooling the glass, and a plurality of machine members and a plurality ofprogrammable controllers moveable under the control of a program tocause relative movement of the tool so as to cause the tool to movealong a programmed path relative to the glass; placing glass havingedges on the machine; loading the data for a programmed path into acontroller; attaching a sensor to the tool assembly and positioning itover the glass; initiating a measuring cycle of the glass; moving thesensor to a check point on the glass; finding the edges of the glasswith the sensor; checking points with established data for programmedpath; using data from check points to calculate offsets and tool path;starting a tooling process on the glass.
 20. A process according toclaim 19 wherein the tooling process is the process of edge grinding theglass with an edge grinder.
 21. A process according to claim 1 9 whereinthe step of finding the edges with the sensor is moving the sensor overthe edges of the glass and recording the position of the sensortransition.
 22. A process according to claim 19 wherein a laser findsthe edges of the glass.